Lisa Dellefave

The genetics of dilated cardiomyopathy

Purpose of review More than 40 different individual genes have been implicated in the inheritance of dilated cardiomyopathy. For a subset of these genes, mutations can lead to a spectrum of cardiomyopathy that extends to hypertrophic cardiomyopathy and left ventricular noncompaction. In nearly all cases, there is an increased risk of arrhythmias. With some genetic mutations, extracardiac manifestations are likely to be present. The precise genetic cause can usually not be discerned from the cardiac and/or extracardiac manifestations and requires molecular genetic diagnosis for prognostic determination and cardiac care. Recent findings Newer technologies are influencing genetic testing, especially cardiomyopathy genetic testing, wherein an increased number of genes are now routinely being tested simultaneously. Although this approach to testing multiple genes is increasing the diagnostic yield, the analysis of multiple genes in one test is also resulting in a large amount of genetic information of unclear significance. Summary Genetic testing is highly useful in the care of patients and families, as it guides diagnosis, influences care and aids in prognosis. However, the large amount of benign human genetic variation may complicate genetic results and often requires a skilled team to accurately interpret the findings.

Altered chromosomal positioning, compaction, and gene expression with a lamin A/C gene mutation.

Background Lamins A and C, encoded by the LMNA gene, are filamentous proteins that form the core scaffold of the nuclear lamina. Dominant LMNA gene mutations cause multiple human diseases including cardiac and skeletal myopathies. The nuclear lamina is thought to regulate gene expression by its direct interaction with chromatin. LMNA gene mutations may mediate disease by disrupting normal gene expression. Methods/Findings To investigate the hypothesis that mutant lamin A/C changes the laminas ability to interact with chromatin, we studied gene misexpression resulting from the cardiomyopathic LMNA E161K mutation and correlated this with changes in chromosome positioning. We identified clusters of misexpressed genes and examined the nuclear positioning of two such genomic clusters, each harboring genes relevant to striated muscle disease including LMO7 and MBNL2. Both gene clusters were found to be more centrally positioned in LMNA-mutant nuclei. Additionally, these loci were less compacted. In LMNA mutant heart and fibroblasts, we found that chromosome 13 had a disproportionately high fraction of misexpressed genes. Using three-dimensional fluorescence in situ hybridization we found that the entire territory of chromosome 13 was displaced towards the center of the nucleus in LMNA mutant fibroblasts. Additional cardiomyopathic LMNA gene mutations were also shown to have abnormal positioning of chromosome 13, although in the opposite direction. Conclusions These data support a model in which LMNA mutations perturb the intranuclear positioning and compaction of chromosomal domains and provide a mechanism by which gene expression may be altered.

Familial dilated cardiomyopathy caused by an alpha-tropomyosin mutation: the distinctive natural history of sarcomeric dilated cardiomyopathy.

OBJECTIVES We sought to further define the role of sarcomere mutations in dilated cardiomyopathy (DCM) and associated clinical phenotypes. BACKGROUND Mutations in several contractile proteins contribute to DCM, but definitive evidence for the roles of most sarcomere genes remains limited by the lack of robust genetic support. METHODS Direct sequencing of 6 sarcomere genes was performed on 334 probands with DCM. A novel D230N missense mutation in the gene encoding alpha-tropomyosin (TPM1) was identified. Functional assessment was performed by the use of an in vitro reconstituted sarcomere complex to evaluate ATPase regulation and Ca(2+) affinity as correlates of contractility. RESULTS TPM1 D230N segregated with DCM in 2 large unrelated families. This mutation altered an evolutionarily conserved residue and was absent in >1,000 control chromosomes. In vitro studies demonstrated major inhibitory effects on sarcomere function with reduced Ca(2+) sensitivity, maximum activation, and Ca(2+) affinity compared with wild-type TPM1. Clinical manifestations ranged from decompensated heart failure or sudden death in those presenting early in life to asymptomatic left ventricular dysfunction in those diagnosed during adulthood. Notably, several affected infants had remarkable improvement. CONCLUSIONS Genetic segregation in 2 unrelated families and functional analyses conclusively establish a pathogenic role for TPM1 mutations in DCM. In vitro results demonstrate contrasting effects of DCM and hypertrophic cardiomyopathy mutations in TPM1, suggesting that specific functional consequences shape cardiac remodeling. Along with previous reports, our data support a distinctive, age-dependent phenotype with sarcomere-associated DCM where presentation early in life is associated with severe, sometimes lethal, disease. These observations have implications for the management of familial DCM.

Sarcomere Mutations in Cardiomyopathy with Left Ventricular Hypertrabeculation

Background— Mutations in the genes encoding sarcomere proteins have been associated with both hypertrophic and dilated cardiomyopathy. Recently, mutations in myosin heavy chain (MYH7), cardiac actin (ACTC), and troponin T (TNNT2) were associated with left ventricular noncompaction, a form of cardiomyopathy characterized with hypertrabeculation that may also include reduced function of the left ventricle. Methods and Results— We used clinically available genetic testing on 3 cases referred for evaluation of left ventricular dysfunction and noncompaction of the left ventricle and found that all 3 individuals carried sarcomere mutations. The first patient presented with neonatal heart failure and was referred for left ventricular noncompaction cardiomyopathy. Genetic testing found 2 different mutations in MYBPC3 in trans. The first mutation, 3776delA, Q1259fs, rendered a frame shift at 1259 of cardiac myosin-binding protein C and the second mutation was L1200P. The frameshift mutation was also found in this mother who displayed mild echocardiographic features of cardiomyopathy, with only subtle increase in trabeculation and an absence of hypertrophy. A second pediatric patient presented with heart failure and was found to carry a de novo MYH7 R369Q mutation. The third case was an adult patient with dilated cardiomyopathy referred for ventricular hypertrabeculation. This patient had a family history of congestive heart failure, including pediatric onset cardiomyopathy where 3 individuals in the family were found to have the MYH7 mutation R1250W. Conclusion— Genetic testing should be considered for cardiomyopathy with hypertrabeculation.

Genetic studies of autosomal recessive primary microcephaly in 33 Pakistani families: novel sequence variants in ASPM gene

Human autosomal recessive primary microcephaly (MCPH) is a rare genetic disorder in which affected individuals are born with reduced brain size. MCPH is genetically heterogeneous, with six loci and four genes reported to date. Mutations in the ASPM gene at the MCPH5 locus appear to be the most common cause of MCPH. For this study, 33 Pakistani families with primary microcephaly were enrolled. Genotyping using microsatellite markers linked to the six known MCPH loci showed the linkage of 18 families to the MCPH5 locus, two to the MCPH2 locus, two to the MCPH4 locus, and one to the MCPH6 locus. The remaining ten families were not linked to any of the known loci. Families linked to the MCPH5 locus were further subjected to screening of the ASPM gene with direct DNA sequencing. Two previously reported variants, 3978G>A (W1326X) and 9557C>G (S3186X), were observed in five Pakistani families. Four novel nonsynonymous sequence variants, 9118insCATT, 9238A>T (L3080X), 9539A>C (Q3180P), and 1260delTCAAGTC, were found to segregate within four families, but were not observed in 200 Pakistani control chromosomes. One of the variants, 9539A>C (Q3180P), occurred in the IQ 79 domain, but its functional significance awaits definition.

A rare Cu/Zn superoxide dismutase mutation causing familial amyotrophic lateral sclerosis with variable age of onset, incomplete penetrance and a sensory neuropathy

We present three members of a pedigree with familial amyotrophic lateral sclerosis (FALS) who have a rare mutation in exon 4 of Cu/Zn superoxide dismutase (SOD1) codon position 89, converting alanine to valine. This mutation was associated with incomplete penetrance and variable age of onset. The onset of the disease was late in two of our patients and early in the other. Two of our patients had symptoms and/or signs of an associated painful sensory neuropathy. The incomplete disease penetrance seen with this mutation (and others reported in the literature) emphasizes the potential value for obtaining an SOD1 genotype in patients with ALS, even if there is no apparent family history.

Lack of association of VEGF promoter polymorphisms with sporadic ALS

The authors tested the association of three vascular endothelial growth factor (VEGF) promoter polymorphisms with sporadic ALS (SALS) to verify the results of a previous study and to investigate their modifier effects on the subphenotypes of SALS in a large family-based and case-control cohort of North American white subjects (N = 1,603). They did not find any association of the VEGF promoter polymorphisms with SALS or its subphenotypes, suggesting that they do not have a direct causal role in ALS.

Cost-effectiveness of population-based BRCA1/2 testing and ovarian cancer prevention for Ashkenazi Jews: A call for dialogue

Purpose: About half of unaffected BRCA1/2 carriers have a negative family history, confounding efforts toward presymptomatic carrier identification. Ovarian cancer is preventable for known carriers but is otherwise highly lethal. Cost-effectiveness and gains in life expectancy are important factors in evaluating the desirability of population-based genetic screening, currently the only viable strategy to identify carriers with unrevealing family histories.Methods: Cost-utility analysis for a population-based genetic screening program offered to American Ashkenazi Jewish women aged 35–55 years measuring cancer incidence, life expectancy, and cost.Results: Our model predicts that a genetic screening program would result in 2811 fewer cases of ovarian cancer, with a life expectancy gain of 1.83 quality-adjusted life years among carriers. At a cost of

Sarcomere mutations in cardiogenesis and ventricular noncompaction.

460 for founder mutation testing, the cost of the program is

Sarcomere Mutations in Cardiomyopathy, Noncompaction, and the Developing Heart

8300 (discounted) per year of quality-adjusted life gained.Conclusion: In populations with a high prevalence of BRCA1/2 founder mutations, genetic screening may be cost-effective when compared with recommended public health interventions such as mammographic screening. We advocate the initiation of a dialogue among Jewish stakeholders, genetics professionals, and public health leaders to determine whether a population-based BRCA1/2 genetic screening program should be pursued.